~ Scientifically Based Lake Restoration, Management & Protection

Watershed BMPs Do Not Restore Polluted Lakes

Dick Osgood, co-founder of Lake Advocates, has authored a scientific publication, Inadequacy of best management practices for restoring eutrophic lakes in the United States: Guidance for policy and practice, published in Inland Waters, the journal of the International Society of Limnology (available at:

“Inland Waters is a peer-reviewed, scholarly journal for original papers that advance lake science and promotes the understanding and sound management of aquatic ecosystems,” according to Dr. Jack Jones, Editor of Inland Waters.

Lake quality in the United States (US) has not significantly changed since the establishment of the Clean Water Act in 1972. Eutrophication, the enrichment of lakes by nutrients through pollution, has been and continues to be problematic, mostly by impairing lakes aesthetically as well as impacting public health. Early success occurred in the nation’s largest lakes following the treatment or diversion of sewage inputs. However, there were an equal number of failures – cases where lake quality did not improve.

There are many more lakes in the US not impacted by sewage. In these lakes, agricultural and urban runoff supplies the excess nutrients, especially phosphorus (P). Thus, the restoration paradigm has focused on reducing pollution in runoff. Runoff pollution is also known as nonpoint source pollution.

Mitigating runoff pollution has relied mainly on Best Management Practices, or BMPs, which are landscape features that intercept runoff. Examples of BMPs include detention ponds, restored wetlands, filter strips and buffers.

According to Osgood, “There are precious few cases where watershed management emphasizing BMPs have resulted in lakes improving and meeting water quality standards.” This is due to the induced changes in these lakes where either internal phosphorus loading has become significant or watershed phosphorus loading from runoff is excessive, 10 to 20 times greater than pre-land-use background conditions – often both occur.

In most cases, restoring eutrophic lakes requires P reductions of 80% or more. Osgood found that BMPs, individually and categorically, fell far short of this. This explains the lack of positive outcomes.

Osgood found that P removal efficiency, the percentage of inflowing P retained, was inadequate for restoring lakes, and in many cases, inadequate for improving lake quality. By evaluating published studies, Osgood found that BMP efficiency was over-stated due to uncertain or limited data, based on inappropriate metrics, misapplying performance from different regions, or projecting long-term performance from short-term studies. In addition, watershed managers often rely on overly optimistic performance measures and seldom conduct field validations.

According to G. Dennis Cooke of Kent State University and Eugene B. Welch of the University of Washington. “Richard Osgood makes an important, evidence-based, point in this manuscript about BMPs and lake management. With regular maintenance, some BMPs are valuable and necessary lake protectors, but alone are unlikely to produce a timely return of a eutrophic lake to a significantly less productive state, especially if residual sediment P internal loading persists. In our view, if external loading has been sharply reduced, sediment P release is usually the next target.”

Osgood estimates that under ideal conditions, BMPs may achieve 50% P reductions, but to do so, many stars need to align. 50% P reductions may be possible if BMPs are a) selected, designed and constructed according to strict criteria, b) maintained regularly, and c) deployed throughout the watershed. As these conditions seldom occur in practice, Osgood found that 25% P reductions are more likely to be the best in real world conditions – well short of the 80% reductions that are required.

Dr. Harry Gibbons, Lake Advocates co-founder says, “Dick and I founded Lake Advocates to help assure that our nation’s lakes are protected and restored using tools and techniques that are based on sound science. This paper embodies our philosophy as it has been subject to the highest standard of scientific rigor.”

Osgood describes two alternative approaches to restore polluted lakes that are more effective, faster and often, cheaper.

Many eutrophic lakes are unresponsive to reductions in nutrient inputs due to the accumulation of nutrients in the lake muds, which recycles back into the lake in the summer. Chemical precipitants have been shown to effectively mitigate recycled P, allowing lakes to recover. Such treatments are safe, quick and cost-effective – often a small fraction of BMP costs.

Engineered or chemically-enhanced treatment systems placed at the mouth of polluted inflows have led to P reductions of 90% or more, often sufficient to restore polluted lakes. These systems function like on-shore (or near-shore) water treatment plants. On a per pound basis, these systems are often much cheaper than BMPs.

Osgood recommends changes in policy that emphasize these other approaches for more effective, outcome-based lake management. BMPs may be used to as supplements to, but not substitutes for, an overall approach for restoring polluted lakes. BMPs have been effective in preventing eutrophication in some cases.